Cancer research has increasingly applied the techology of flow cytometry to study the physical and functional characteristics of neoplastic and normal cells. As flow cytometry has developed its capabilities to separate cells based on fluorescence and light scatter, both clinical and basic scientists in cancer research have used this instrumentation to analyze and sort different populations of cells. Such parameters as membrane, cytoplasmic and nuclear antigen expression, various light scattering properties, DNA content and cell cycle analysis, the detection of apoptosis, as well as the measurement of intracellular biochemical changes such as calcium flux and changes in pH are within the realm of current flow cytometry technology. More recently, the development of fluorescent proteins which can be expressed under control of different promoters has expanded the capabilities of flow cytometry and provided a powerful tool for molecular biologists to sort subpopulations of cells. Each of the approaches outlined here is represented in the cancer immunology and molecular biology projects outlined in this proposal to support a Flow Cytometry Facility which supports the Cancer Center members at the Markey Cancer Center. This is a well established facility which has been essential to the development of Cancer Center research programs. The facility currently contains a FACSCalibur and FACStar Plus and will be upgraded in the Spring, 1999 with either a MoFlo or a Vantage SE. While we anticipate continued support from the Cancer Center and the University, NIH support for the facility will enable us to maintain rates that promote faculty usage and stability of the facility personnel.